Since the track width of a magnetic disk is decreased with increase of recording density in the magnetic disk device, a substantial further improvement of preciseness of a head positioning is required in a magnetic head tester or a magnetic disk tester. Further, the rotation number of a disk is increased from 5400 rpm to a range from 700 rpm to 15000 rpm, or more, recently.
U.S. Pat. No. 7,035,039 (corresponding to JP-2003-272326A of the present applicant) discloses a technique in which a piezo actuator is provided between a suspension spring and a head carriage and a head assembly is driven by the piezo actuator according to a servo signal.
In the invention disclosed in U.S. Pat. No. 7,035,039, deviation of the magnetic head (referred to as “head”, hereinafter) positioned in a predetermined track from a center of the track is corrected by finely moving a light weight head cartridge, which supports a head assembly, according to a servo signal or dynamically moving (rotating) the head assembly within the head cartridge according to the servo signal. The fine movement is achieved by moving the head, for example, several microns at high speed with respect to a track, so that positional correction of the head is performed highly precisely at high speed according to the servo signal in such a way that the head becomes an ON track state on the track or a predetermined position of the track.
In one of the embodiments of U.S. Pat. No. 7,035,039, the ON track positioning of the head is performed by finely moving the head cartridge mounted on a piezo stage for finely adjusting a position of the head and then dynamically rotating the head assembly provided in the head cartridge to the ON track state according to the servo signal.
This head assembly is axially supported by a cylindrical member and swung around an axis of the cylindrical member by the piezo actuator. Since the piezo actuator finely moves the head in such a way that deviation of the head from the track center is corrected, a swinging mechanism of the head assembly makes the head possible to respond to the servo signal at high speed.
However, since the number of tracks per inch is increased to several thousands recently, higher preciseness of servo control and higher speed movement of the head of the rotation mechanism of the head assembly are required. However, since a mass of a rotary portion of the previously described system in which the head assembly is swung around the cylindrical member is large, it is necessary to rotate a disk by one or more until the position of the head is corrected to an ON track state. Therefore, there is a problem that read/write of a test data takes time. Consequently, it is necessary to further improve the response speed of the head in the ON track control.